1. Field of the Invention
The present invention relates to an electrically-operated (so-called by-wire-type) hydraulic control device which can smoothly increase and decrease a fluid pressure in a hydraulic control circuit. The invention also relates to a brake device of a compact, lightweight design which has the above hydraulic control device incorporated in a caliper of a disc brake of a vehicle, an can achieve a smooth hydraulic control such as an anti-lock control and a traction control.
2. Related Art
Recently, in order to provide a vehicle brake device capable of dealing with various brake control modes, there has been developed an electrically-operated (by-wire-type) brake device as disclosed in Post-examined Japanese Patent Publication No. Hei. 4-28931. The vehicle brake device of this type comprises a motor, a speed changer having a planetary gear mechanism, a ball thread and soon. On the other hand, there has also been developed an anti-lock control device of the circulating type as disclosed in Unexamined Japanese Patent Publication No. Hei. 9-164934 in which a motor is operated quite effectively, and the operating sounds or noises of the motor and a pump are made quiet, thereby providing a good operating feeling of a brake pedal.
However, in the construction of the former electrically-operated brake device, a rotational force from the motor is reduced by the speed changer, and then a brake piston is operated through the ball thread. Therefore the response is poor and, in addition to that, the weight and volume of the device are increased, which is disadvantageous in the achievement of a lightweight, compact design. Particularly in case of a disc brake of the type in which a rotary-type motor, an encoder, a speed changer and a hydraulic pressure-generating portion are combined together into a generally unitary construction, the device becomes more bulky than a hydraulic brake, used in current passenger cars, if these component parts are merely connected together. Therefore there suffers from a problem that the application of this device is limited because of a currently-available device-mounting space.
In the latter anti-lock control device, the motor can be operated quite effectively, and the sounds or noises of the motor and pump can be made quiet. However, in this device, a relief valve and so on are required and a path of piping is accordingly complicated. Further, there would raise a problem of the occurrence of the pulsations which are undesirable from the performance point of view.